Adults grow new fat cells, researchers find

The good news is that about 10 per cent of our fat cells die
each year. The bad news is that the same amount of new ones are
produced annually to replace them, scientists have found.

The discovery of this cell turnover throughout life could lead
to a new approach to tackling obesity, if drugs can be developed
that prevent new fat cells from forming.

It could also help explain why it is so difficult to keep the
kilograms off after slimming, because there is no net loss of fat
cells after weight loss, an international team of researchers
co-led by Peter Arner of the Karolinska Institute in Sweden has
found.

"The new fat cells generated during and after weight reduction
need to fill up their lipids rapidly," Dr Arner said. This could
increase appetite, he said.

The team studied more than 680 lean and obese adults and found
that the number of their fat cells remained constant during
adulthood, with the fatter people having about 50 per cent more fat
cells than the thinner ones.

To see whether dramatic weight loss reduced the number of cells,
the team studied obese people who underwent surgery to reduce the
size of their stomachs.

They found the number of fat cells was unchanged after the
operation, but they had shrunk to a smaller volume.

Dr Arner said this meant the difference in the number of fat
cells between lean and obese people was established in childhood
and adolescence. Eating more or less as an adult simply made them
swell or shrink.

"Changes in fat mass in adulthood can mainly be attributed to
changes in fat cell volume," he said.

The last part of the study, which is published in the journal
Nature, identified fat cell turnover using a new technique.
Until then it had been unclear whether adults could make new fat
cells.

The researchers measured levels of carbon isotopes in the DNA of
the fat cells of people born before and after the nuclear bomb
testing between 1955 and 1963, which led to a large increase in the
amount of radioactive carbon-14 in the atmosphere around the globe.
Fat tissue was collected during liosuction or abdominal
surgery.

The finding that people whose fat cells were deposited before
testing began contained radioactive matter revealed that new cells
were being produced.

"Approximately 10 per cent of fat cells are renewed annually at
all adult ages and levels of body mass index," Dr Arner said.